Scanning ion beam etch

ABSTRACT

The present disclosure provides a method to adjust asymmetric velocity of a scan in a scanning ion beam etch process to correct asymmetry of etching between the inboard side and the outboard side of device structures on a wafer, while maintaining the overall uniformity of etch across the full wafer.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims the benefit of U.S. Patent Application No.62/666,324, filed on May 3, 2018, the contents of which is incorporatedherein by reference in its entirety.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

n/a

TECHNICAL FIELD

The present disclosure relates to the field of charged particle sourcesincluding plasma sources for direct etching and deposition, broad-beamion sources for ion beam deposition and etching, and electron sourcesfor surface modification.

BACKGROUND

FIG. 1 illustrates an ion beam etch (IBE) system. In an IBE process,wafer 180 is placed in front of an ion source 105. At least one surfaceof the wafer 180 can be exposed to a beam 130. Ion source 105 can becomprised of a plasma chamber 110, and an ion extraction grid system150. Ion extraction grid system 150 is comprised of a plurality ofconducting plates that have multiple holes therein aligned from plate toplate. Grid system 150 extracts and helps collimate ion beamlets comingout of each of the holes of the plates, and forms a substantiallycollimated ion beam 130. Plasma in the plasma source may be generated bymethods known in the art including direct current (DC) and radiofrequency (RF) inductively coupled plasma (ICP) coils 160. The energy ofthe ions extracted from the ion source 105 is defined by the voltagesapplied to the grid system 150.

An electron source 230, may be placed between the ion extraction gridsystem 150 and a wafer stage to prevent charge damage from the impingingions on the wafer. Wafer 180, is placed on wafer stage 140. The stage140 can rotate the wafer about a central axis 220. The stage 140 cantilt the wafer 180 with respect to the ion beam 130 for at least aportion of the etching process. Ions from the beam 130 can be directedat any angle with respect to the wafer surface by tilting the wafer 180.Any solid material can be etched with an IBE process. Provisions may bemade on the wafer stage 140 to cool the wafer 180 during the etchingprocess to prevent thermal damage to the devices on the wafer 180. Wafer180 may also be heated to a specific temperature to enhance the ion beametching process.

A typical wafer 180 can include many devices and may be covered withphotoresist masks or other type of masks. The devices can be processedwith ion beam exposure to etch the desired shape of the devices on thewafer 180. The desired shape of the devices can be achieved by adjustingprocess parameters including, for example: wafer tilt angle during etch,duration of etch, beam energy, beam current, Photoresist mask sidewallangles, wafer temperature, etc. An end point detector 240 may be placedin line of sight of the wafer 180 when the devices are made ofmultilayer materials and precise end pointing of the etch at apredetermined layer is often desired.

The devices on wafer 180 being etched are expected to show similarshapes (e.g., sidewall profiles, etc.) However, devices can showdifferent shapes depending on the location of the devices on the wafer180. One example of a specific type of shape difference is calledinboard and outboard asymmetry. FIGS. 2a-2c show a schematicrepresentation of the asymmetry of the inboard (IB) side 191 of a deviceand the outboard (OB) side 192 of a device after ion beam etching. Theasymmetry may be quantified as the sidewall angle differences on oneside α versus the opposite side β. FIG. 2a shows symmetric etching. FIG.2b and FIG. 2c show asymmetric etching.

The asymmetry of the IB side 191, and the OB side 192 of devices in ionbeam etching often has a specific relationship to the tilting of thewafer 180. This relationship is shown in FIGS. 3a-3b . FIG. 3a is a topview of a wafer 180 being etched. The tilt axis runs along the diagonalof the wafer as shown with respect to the wafer top view. In FIG. 3a ,wafer 180 is being etched by an ion beam impinging on it from adirection perpendicular to the plane of the paper. FIG. 3b is a crosssection view of FIG. 3a along the wafer diagonal perpendicular to thetilt axis. In FIG. 3b , the wafer cross-section, direction of tilt axisruns along the middle of the wafer, and perpendicular to the plane ofthe paper. Asymmetry between the IB side 191 of the device and the OBside 192 of the device can be seen on the devices located towards thetop and bottom of the wafer 180. The asymmetry becomes more pronouncedthe further away the device is from the tilt axis, and as the tilt angleis increased, e.g., the wafer 180 is tilted further from the normalangle of incidence of the incident beam.

In a perfect ion source, and grid system, all beamlets would beperfectly collimated, with no divergence of the ions from the intendeddirection. In such a system, all features etched on the wafer 180 wouldbe perfectly symmetrical. Practical ion beam etch systems have non-zerobeam divergence.

In practice, ion sources generate an ion beam that is a collection ofbeamlets with a finite non-zero beam divergence, as illustrated in FIG.4. Beamlet divergence 131 is shown in this figure. A consequence of thebeamlet divergence is that as the wafer is tilted away from normal beamincidence, there will be more intense etching on the side of the wafer180 nearer to the ion source, and less intense etching on the side ofthe wafer 180 farther from the ion source. By rotating the wafer 180about an axis 220, the etch depths can be made more uniform in the areasof the wafer 180 that are feature free. Devices on the wafers 180however are typically made of features in 3-dimensions and not flatsurfaces. On 3-dimensional features on the wafer 180, the effect of thetilting of the wafer 180 away from normal beam incidence, in conjunctionwith beam divergence, is that the inboard side 191 of the devices on thewafer 180 will experience a different amount of beam exposure than theoutboard side 192 of the devices. This inboard and outboard asymmetrybecomes more pronounced as the location of the devices is farther awayfrom the tilt axis of the wafer 180, and as the tilt angle is increasedaway from normal beam incidence.

Translating (e.g., scanning) the wafer 180 across the beam can addressasymmetry between the inboard side 191 of the device and the outboardside 192 of the device. In FIG. 5, the region marked by double endedarrow 550 is the region where ion beam exposure of the wafer occurs. Asingle instance of translation of the wafer, translation starting at anypoint where all regions of the wafer is outside of the region shown by550, translation path taking the wafer through the region represented by550, is considered one scan. In FIG. 7, region 550, where ion beamexposure occurs is defined through the introduction of physical beamblocks 171, and 172.

In some embodiments, the path of the wafer 180 during translation isdefined as the scan path. The scan path can be within a plane that isparallel (or nearly parallel) to the plane of the tilted wafer surfacefor at least one scan. The scan path of wafer translation can be linearfor at least one scan. The path of wafer translation can be non-linear(e.g., curved) for at least one scan. The scan path can be parallel tothe tilted wafer 180 for at least one scan. The wafer tilt can beconstant during the scan path for at least one scan. The wafer tilt canvary along the path of the scan for at least one scan. The scan path canbe parallel to the wafer 180 during at least one point in the scan forat least one scan. The scan path can be parallel to the wafer 180 at allpoints during the scan for at least one scan. The scan path can be in adifferent plane than the wafer 180 for at least one scan. The scan pathcan be within a plane that is parallel (or nearly parallel) to the planeof the tilted wafer surface for all scans. The scan path of wafertranslation can be linear for all scans. The path of wafer translationcan be non-linear (e.g., curved) for all scans. The scan path can beparallel to the tilted wafer 180 for all scans. The wafer tilt can beconstant during the scan path for all scans. The wafer tilt can varyalong the path of the scan for all scans. The scan path can be parallelto the wafer 180 during at least one point in the scan for all scans.The scan path can be parallel to the wafer 180 at all points during thescan for all scans. The scan path can be in a different plane than thewafer 180 for all scans.

SUMMARY OF THE INVENTION

In accordance with an embodiment, the present disclosure relates tousing asymmetric scanning velocity in an ion beam etch process tocorrect asymmetry of etching between the inboard side and the outboardside of device structures on a wafer while maintaining the overalluniformity of etch across the full wafer.

In accordance with another embodiment, the present disclosure relates tousing asymmetric scanning velocity in an ion beam etch process togenerate exaggerated asymmetry of etching between inboard and outboardsides of devices on a wafer, while maintaining the overall uniformity ofetch across the full wafer.

In accordance with another embodiment, the present disclosure relates tousing symmetric velocity scanning to enable control of inboard andoutboard asymmetry even when the ion beam system is configured with asmall ion source, and small grids. Without asymmetric velocity scanning,the ion source and grids will need to be of a lateral dimension largerthan the sum of the wafer diameter, two times the beamlet divergenceprojected on the plane of the scan, and the ion beam density will needto be highly uniform across the lateral dimension.

In accordance with another embodiment, the present disclosure relates tousing asymmetric velocity scans combined with symmetric velocity scansto address the inboard and outboard asymmetry and wafer etch uniformity,where the number of scans needed to finish the etch process may be asingle scan or multiple scans.

In accordance with another embodiment, the present disclosure relates toa process whereby scan motion may be a straight linear motion of thewafer center across the ion beam or may include slight deviations fromstraight lines such as curved paths of motion of the wafer center acrossthe ion beam.

In accordance with another embodiment, the present disclosure relates toan alternative to asymmetric velocity scan motion of the wafer where theion beam current or the ion beam voltage is modulated as the wafer movesacross the ion beam. The wafer may be exposed to either larger beamcurrent or higher beam voltage when the wafer center is scanning on thefar side of the scan beyond the mid-plane of the ion source.

In accordance with another embodiment, the present disclosure relates toan alternative to an asymmetric velocity profile scan by modulating thepath of the scan, so that the wafer spends more time exposed to the ionbeam on the far side of the scan after the wafer has passed themid-plane of the ion source.

In accordance with another embodiment, the present disclosure relates toan alternative to the asymmetric velocity scan of the wafer across anion beam by placing beam blocks in an asymmetric fashion with respect tothe mid-plane of the ion source and grids, so that the wafer spends moretime exposed to the ion beam on the far side of the scan even with thesymmetrical velocity profile of the scan.

According to one aspect of an embodiment of the present disclosure, amethod of correcting asymmetry during a wafer etching process isprovided, where the method includes producing a plasma from a plasmasource, the plasma source comprising a plasma chamber and an ionextraction grid system, the ion extraction grid system configured toproduce an ion beam from the plasma, the ion beam having a central axis,supporting a wafer on a stage, scanning the wafer relative to the ionbeam along a scan path, and modifying applied beam flux as a function ofa position of the wafer.

According to another aspect of an embodiment of the present disclosure,a method of correcting asymmetry during a wafer etching process isprovided, where the method includes producing a plasma from a plasmasource, the plasma source comprising a plasma chamber and an ionextraction grid system, the ion extraction grid system configured toproduce an ion beam from the plasma, the ion beam having a central axis,supporting a wafer on a stage including at least one of rotating thestage about the central axis and tilting the stage with respect to theion beam during at least a portion of the etching process, scanning thewafer relative to the ion beam along a scan path in accordance with ascan velocity function, and modifying applied beam flux as a function ofa position of the wafer by varying the scan velocity function as thewafer travels along the scan path.

According to another aspect of an embodiment of the present disclosure,a method of correcting asymmetry during a wafer etching process isprovided, where the method includes producing a plasma from a plasmasource, the plasma source comprising a plasma chamber and an ionextraction grid system, the ion extraction grid system configured toproduce an ion beam from the plasma, the ion beam having a central axis,supporting a wafer on a stage, scanning the wafer relative to the ionbeam along a scan path, the scan path comprising a scan out path fromthe first end of the ion beam to the second end of the ion beamaccording to a scan out velocity function and a scan back path from thesecond end of the ion beam to the first end of the ion beam according toa scan back velocity function, wherein one of the scan out velocityfunction and the scan back velocity function varies as a function oftime, and modifying applied beam flux as a function of a position of thewafer.

According to another aspect of an embodiment of the present disclosure,a method of correcting asymmetry during a wafer deposition process isprovided, where the method includes producing a plasma from a plasmasource, the plasma source comprising a plasma chamber and an ionextraction grid system, the ion extraction grid system configured toproduce an ion beam from the plasma, the ion beam having a central axis,supporting a wafer on a stage, scanning the wafer relative to the ionbeam along a scan path, and modifying applied beam flux as a function ofa position of the wafer.

Additional features and advantages of the disclosure will be set forthin the description which follows, and in part will be obvious from thedescription, or can be learned by practice of the herein disclosedprinciples. The features and advantages of the disclosure can berealized and obtained by means of the instruments and combinationsparticularly pointed out in the appended claims. These and otherfeatures of the disclosure will become more fully apparent from thefollowing description and appended claims, or can be learned by thepractice of the principles set forth herein.

BRIEF DESCRIPTION OF THE DRAWINGS

In order to describe the manner in which the above-recited and otheradvantages and features of the disclosure can be obtained, a moreparticular description of the principles briefly described above will berendered by reference to specific embodiments thereof which areillustrated in the appended drawings. Understanding that these drawingsdepict only exemplary embodiments of the disclosure and are nottherefore to be considered to be limiting of its scope, the principlesherein are described and explained with additional specificity anddetail through the use of the accompanying drawings in which:

FIG. 1 illustrates an ion beam etch system;

FIG. 2a illustrates symmetric etching;

FIG. 2b illustrates asymmetric etching;

FIG. 2c illustrates asymmetric etching;

FIG. 3a is a top view of a wafer 180 being etched;

FIG. 3b is a cross section view of FIG. 3a along the wafer diagonalperpendicular to the tilt axis;

FIG. 4 illustrates ion beam divergence;

FIG. 5 illustrates an improved scanning ion beam etch system accordingto an embodiment of the present disclosure;

FIG. 6 illustrates an improved scanning ion beam etch system accordingto an embodiment of the present disclosure;

FIG. 7 illustrates an improved scanning ion beam etch system accordingto an embodiment of the present disclosure;

FIG. 8 illustrates variable scan velocity according to an embodiment ofthe present disclosure;

FIG. 9 illustrates relative etch from the wafer center with constantscan velocity and variable scan velocity according to an embodiment ofthe present disclosure;

FIG. 10a illustrates beamlet divergence and effect of divergence on theinboard side of the wafer versus the outboard side of wafer as the waferis scanned across beam according to an embodiment of the presentdisclosure;

FIG. 10b illustrates beamlet divergence and effect of divergence on theinboard side of the wafer versus the outboard side of wafer as the waferis scanned across beam according to an embodiment of the presentdisclosure;

FIG. 11a illustrates a beam that has a higher flux at the center of thebeam;

FIG. 11b illustrates a uniform beam where the flux is independent ofposition in the beam;

FIG. 12 illustrates the mid-plane of the source and far side of scanwhere preferential etching of the outboard side of devices occurs;

FIG. 13 illustrates one type of asymmetric velocity profile (solidlines) that preferentially etches the outboard side on the far side ofthe scan compared with a symmetric velocity (dashed lines) scan;

FIG. 14 illustrates the mid-plane of the source, and near side of scanwhere preferential etching of the inboard side of the devices occurs;and

FIG. 15 illustrates one type of an asymmetric velocity profile that is astep type (solid lines) that preferentially etches the outboard side onthe far side of the scan compared with an asymmetric velocity profilethat is smoothly changing type (dashed lines) scan.

Similar reference characters refer to similar parts throughout theseveral views of the drawings.

DETAILED DESCRIPTION

FIG. 5 shows an illustration of an improved scanning ion beam etch (IBE)system of the present disclosure. Wafer 180 can be tilted off normalincidence with respect to the ion beam, and scanned across the beamstarting from outside the beam on one end to the outside of the beam onthe opposite end.

In some embodiments, in order to compensate for a non-uniform beam flux,the wafer scan velocity can be varied during a wafer scan. As shown inFIG. 5, the wafer 180 is typically scanned back and forth in and/orthrough the beam 130. A typical wafer scan can start with the wafer 180in position 500. The wafer 180 is scanned (e.g., translated) through thebeam to position 510. The wafer 180 can then be scanned (e.g.,translated) back through the beam from position 510 to position 500. Thewafer 180 can be stopped (e.g., zero velocity) between scans (at eitheror both positions 500 and 510). The path from position 500 to position510 and back again to position 500 can be a continuous path. The paththe wafer 180 follows scanning from position 500 to position 510 can bethe same as the path the wafer 180 follows scanning from position 510 toposition 500. The path the wafer 180 follows scanning from position 510to 500 can be different from the path the wafer 180 follows scanningfrom position 500 to position 510.

The wafer 180 in position 500 and/or position 510 can be at leastpartially exposed to the beam. The wafer 180 in position 500 and/orposition 510 can be completely exposed to the beam. The wafer 180 inposition 500 and/or position 510 can be at least partially outside(e.g., not exposed to) the beam. The wafer 180 in position 500 and/orposition 510 can be completely outside (e.g., not exposed to) the beam.The position of 500 and/or 510 can be invariant between at least twoscans. The position 500 and/or 510 can be invariant for more than twoscans. The position 500 and/or 510 can be invariant for all scans. Theposition of 500 and/or 510 can be changed between at least two scans.The position 500 and/or position 510 can be changed between more thantwo scans. The position 500 and/or position 510 can be changed betweenevery scan. The length of the wafer scan (e.g., the distance betweenpoint 500 and 510) can be constant for at least 2 scans. The length ofthe wafer scan be constant for all scans. The length of the wafer scancan be different between at least 2 scans. The length of the wafer scancan be different in more than 2 scans. The length of the wafer scan canbe different for all wafer scans.

In some embodiments, at least a portion of the wafer 180 can start thescan outside the ion beam. All of the wafer 180 can start the scanoutside the ion beam. A portion of the wafer 180 can be exposed to thebeam during a scan. All of the wafer 180 can be exposed to the beamduring the scan. A portion of the wafer 180 can be outside the beam(e.g., not exposed to the beam) at the end of a scan. All of the wafer180 can be outside of the beam (e.g., not exposed to the beam) at theend of a scan. In one embodiment, the wafer 180 is not exposed to thebeam at the start of a scan, a portion of the wafer 180 is exposed tothe beam during the scan, and the wafer 180 is not exposed to the beamat the end of the scan. The wafer 180 can be scanned back and forth at adesired tilt angle with respect to the ion beam. The wafer 180 can berotated about an axis 220 as it is scanned across the beam. The rotationspeed can be constant during the scan. The rotation speed can varyduring the scan. The process of scanning at fixed scan velocity canrepeated until the desired etch depth is achieved. The scan path can becentered in the beam (e.g., the midpoint of the scan approximatelycoincides with the center of the beam). The scan path can be offset inthe ion beam (e.g., the midpoint of the scan does not coincide with thecenter of the beam).

This scanning method addresses the inboard and outboard asymmetryarising from the tilt of the wafer 180 and the divergence of thebeamlets that cause the near side of the wafer 180 to be etched at ahigher rate than the far side of the wafer 180 in a conventional ionbeam etch (IBE) machine.

Many ion beam operations, such as, ion beam smoothing, sidewall etching,and sidewall cleaning, require a large tilt angle with respect to theion beam. The wafer 180 can be tilted greater than approximately 10degrees off normal incidence of the ion beam. The wafer 180 can betilted greater than 30 degrees off normal incidence of the ion beam.Scanning at large tilt angles as shown in FIG. 6, can result in themid-point of the scan moving further away from the ion source, and thescan length increasing in order to be able to scan the wafer 180 acrossthe ion beam. The increased scan length and the larger distance betweenthe wafer 180 and the source can be difficult to accommodate in a HighVacuum/Ultra High Vacuum Chamber.

The required scan length can be decreased by inserting physical blocks,171 and 172, towards the ends of the scan, as shown in FIG. 7. Theblocks 171 and 172 form an aperture that narrows the beam 130, thuscreating a portion or “slit” of the ion beam through which the wafer 180is scanned. The blocks 171 and 172 may be inserted symmetrically withrespect to the mid-plane 310 of the ion source 105 and ion extractiongrid system 150 as shown in FIG. 7. The blocks 171 and 172 can beinserted asymmetrically with respect to the mid-plane 310. The slitwidth can be made adjustable by adjusting the positions of the upperblock 171, or the lower block 172, or both. However, in cases wherescanning the wafer 180 across the slit at large tilt angles is required,the distance from the ion extraction grid system 150 to the wafer 180 atits scan midpoint can be much larger than in conventional ion beam etch(IBE) systems.

In practical IBE systems, the beam density of beam 130 can be spatiallynon-uniform. This non-uniformity can be due to beamlet divergence. Thiseffect often increases as the source-to-wafer distance increases and canbe amplified by a large distance between the wafer scan's mid-point.Scanning the wafer 180 through the beam 130 at constant scan velocitycan result in an etch that is highly non-uniform, with the wafer centeretching much faster than the edge of the wafer. Deploying a variablescan velocity, as illustrated in the schematic in FIG. 8, candramatically improve the etch uniformity over the entire wafer 180.Slowing down the velocity of the scan when the wafer 180 is away fromthe midpoint of the scan can enhance the etching at the points of thewafer 180 away from its center.

In some embodiments, the wafer velocity can be changed during the waferscan. The wafer scan velocity can be continuously changing during ascan. The wafer scan velocity can be constant during some portion of ascan. The wafer velocity profile can be identical for at least 2 scans.The wafer scan velocity profile can be identical for all scans. Thewafer scan velocity can change between at least two scans. The waferscan velocity profile can change for each scan. The wafer scan velocitycan be zero during at least one point during the scan. The wafervelocity profile can be symmetric (see FIG. 8 for example). The scanvelocity profile can be monotonic. The scan velocity profile can bediscontinuous.

Examples of symmetric variable velocity to achieve highly uniformetching over the full wafer 180 are shown in FIG. 8. The midpoint of thescan is represented by X=0. The direction of the scan is along thex-axis. The negative x-axis positions are closer to the ion source 105than the positive x-axis positions. Variable velocity, which issymmetric about the mid-point of the scan, is shown in the example inFIG. 8. Symmetric variable velocity of the scan can be used to obtainuniform etching across the wafer 180. The symmetric variable velocityprofile can be a step function, or a smooth function, as shown in theexample in FIG. 8. Symmetric variable velocity as shown in the examplehere is used to obtain uniform etching across the full wafer 180, asshown in FIG. 9.

Scanning the wafer 180 across the beam 130 does not address a secondcause of inboard and outboard asymmetry of devices. This second cause ofasymmetry is caused by the large distance needed to enable the scanningof a tilted wafer 180 across the beam 130, the finite size of the ionsource 105 and ion extraction grid system 150, and the beamletdivergence. This effect is illustrated in FIGS. 10a-10b . At largedistances, the finite lateral size of the ion source 105, and thebeamlet divergences cause the inboard side 191 of the devices to beexposed to larger amount of ions compared to the outboard side of thedevice. This asymmetry is present at all tilt angles. This isillustrated in FIGS. 10a-10b . A rotating wafer 180, as it is beingscanned across the beam 130, causes the outboard side 192 of the device,at the outer edges of the wafer 180, to etch much less than the inboardside 191 of the device as seen in FIGS. 10a-10b . Solid angles projectedfrom the inboard side 191 of the device and the outboard side 192 of thedevice, to the plane of the ion extraction grid system 150, representthe amount of beam exposure on the inboard side 191, and outboard side192 respectively, as the wafer 180 is scanned across the beam 130. Theimbalance of the beam exposure of the inboard side 191 and outboard side192 of the devices can be clearly seen in FIG. 10a and FIG. 10 b.

The inboard and outboard etch asymmetry associated with the finitedimension of the ion source 105 and beamlet divergence can be addressedby making the ion source 105 and grids of ion extraction grid system 150significantly larger in the Y-axis direction, as shown in FIGS. 11a-11b. FIG. 11a shows a beam 130 that has a higher flux at the center of thebeam 130. It is possible to have a beam 130 that has a higher flux atthe edge of the beam 130 than at the center of the beam 130 (not shown).FIG. 11b shows a uniform beam 130 where the flux is independent of theposition in the beam 130. The Y-axis direction is the direction of ascan. Increasing the lateral dimension of the ion source 105 and gridsof the ion extraction grid system 150 to be at least equal to the sum ofwafer diameter and twice the beamlet divergence and making the ion fluxuniform across the lateral dimension, as shown in FIG. 11b , can allowboth the inboard side 191 and outboard side 192 of the devices to beexposed to the same amount of ion beam exposure, and eliminate theasymmetry between the inboard side 191 and outboard side 192 of thedevices.

The non-ideal ion beam shown in FIG. 11a shows an example of when theflux of the ion beam 130 is higher in the center of the beam 130compared to an edge of the beam 130. It is possible to have an ion beam130 where the flux of the ion beam 130 is higher at an edge of the beam130 compared to the center of the beam 130 (e.g., through magneticconfinement of the beam, a non-uniform grid system, etc.). In this case,it may be desirable to increase the dose in the center of the wafer 180compared to the edge of the wafer 180 during a scan. The scan velocityat an end of a scan can be greater than the scan velocity in the centerof the scan (e.g., the scan velocity for at least one point towards theend of the scan is higher than a point toward the center of the scan).

Establishing and sustaining uniform plasma distribution across a largeion source 105 can be practically difficult. Large variations in plasmadensity across the lateral dimensions of the plasma source can bedifficult to address. Large lateral dimension of grids can causefailures arising from mechanical instabilities related to thermalexpansion and contraction cycles of ion source operation. Due toextraordinary challenges associated with larger dimensions of ionsources and large sized grids, it is desirable to address the asymmetryproblem with a smaller ion source, and smaller grids.

Referring to FIG. 12, slowing down the scan velocity when the wafercenter is on the far side of the scan 301 (e.g., wafer scan positionsfarther from the ion beam source 105) can also improve uniformity. Asshown in FIG. 12, the scan velocity can be reduced for at least aportion of points below the mid-plane 310 of the ion source 105 and ionextraction grid system 150. The reduced scan speed enhances the etchingon the outboard side 192 of the devices. By slowing down the scan speedwhen the wafer center is on the far side of the scan, inboard andoutboard asymmetry, which can be present in a symmetric velocity scan,can be improved.

FIG. 13 shows an example of a scan velocity profile described by thesystem of the present disclosure. In the schematic shown in FIG. 13, thepositive x positions are the far side positions 301 of the wafer centerwhere the scan speed is reduced to increase the etching on the outboardside 192 of the device. Overall excellent uniformity of etching acrossthe full wafer 180 is preserved by increasing the scan velocity on thenegative X side of the scan (e.g., when the wafer 180 is closer to theion source 105), than what a symmetric variable scan profile 303requires for good uniformity.

A scan velocity can be a function of the wafer distance from the ionbeam 105 during a scan. A scan velocity can decrease as the distancebetween the wafer 180 and the ion beam 130 increases during a scan. Ascan velocity can increase as the area of the wafer 180 exposed to thebeam 130 increases. A scan velocity can decrease as the area of thewafer 180 exposed to the beam 130 decreases.

In some embodiments, a scan acceleration can vary during a scan. A scanacceleration profile can be asymmetric. A scan acceleration can beidentical between at least 2 scans. A scan acceleration curve is a plotof the wafer acceleration vs. the position of the wafer 180 along thescan path. A scan acceleration curve can be identical for more than 2scans. A scan acceleration curve can be identical for all scans. A scanacceleration curve can be different between at least 2 scans. A scanacceleration curve can be different for more than 2 scans. A scanacceleration curve can be different for all scans. A scan accelerationcan be constant during at least a portion of a scan. A scan velocity canbe selected to maintain a constant dose of ions across at least oneregion of the wafer 180 during a scan. A scan velocity can be selectedto maintain a constant dose of ions across all exposed regions of thewafer 180 during a scan.

Increasing the scan velocity when the wafer center is on the near sideof the scan 302, which are the points above the mid-plane 310 of the ionsource 105 and grid system 150, as shown for example in FIG. 14, reducesthe etching on the inboard side 191 of the devices. In the schematicshown in FIGS. 8, 13, 14 and 15, the negative X positions are on thenear side 302 of the scan. When the wafer center is on the near side302, increasing the scan speed reduces etching on the inboard side 191of the device. Overall excellent uniformity of etching across the fullwafer 180 is preserved by lowering the scan velocity on the positive Xside of the scan. The relationship of such a velocity profile withrespect to a symmetric velocity profile 303 required for good filmuniformity across the wafer 180 is shown in FIG. 13

In some embodiments, the shape of the velocity versus position can be astepped velocity configuration or a smoothly varied configuration,represented by 304 in FIG. 15. An asymmetrical velocity profile causesthe wafer 180 to spend more time on the positive x-side (e.g., furtheraway from the ion source 105) than on the negative x-side, assuring moreetching on the outboard side 192 of devices compared to the inboard side191 of the devices. This process of asymmetric velocity of the scanenables inboard and outboard asymmetry control even when the etchingsystem is configured with an ion source 105 having lateral dimensionssmaller than the sum of wafer diameter and twice the beamlet divergenceprojection on the wafer scan plane.

The inboard side 191 of the device can be preferentially etched byslowing down the scan speed on the near side to correct for asymmetryarising in systems with sources that have a beam of less density at thecenter of the source compared to the density away from the center of thesource.

Exemplary ion beam etch process parameters are as follows.

-   -   Plasma source power approximately in the range of 100 W-5 kW.    -   Process chamber pressures in the range of 1E-3 Torr to 1E-5        Torr.    -   Gas compositions can contain an inert gas (e.g., Ar, Kr, Xe, He,        etc., or mixtures of these).    -   Gas compositions can contain reactive gases (e.g., halogen        containing gases, C_(x)H_(y)F_(z), Cl₂, oxygen containing gases,        O₂, nitrogen containing gases, N₂, NF₃, carbon containing gases,        CH₄, CO, CO₂, sulfur containing gases, SF₆, hydrogen containing        gases, H₂, H₂O, or mixtures of these).    -   Gas compositions can contain a mixture of inert and reactive        gases.    -   Wafer temperature can range from approximately −40 C to 400 C.    -   Wafer scan speeds can range from approximately 0.01 mm/sec to 1        cm/sec. In one embodiment, the wafer scan speeds range from 1        mm/sec to 100 mm/sec.    -   Wafer rotation speeds range from approximately 0.5 RPM to 1000        RPM.    -   Ion beam voltages are typically less than about 500 eV.    -   Wafer tilt angles range from approximately 1 degree (e.g., 1        degree off perpendicular to the ion beam 105) to about 85        degrees (e.g., a glancing angle to the ion beam 105).

Any of the steps and procedures described above, while referred toherein as being included in the etching process, may also be applied toa deposition process.

Although a variety of examples and other information was used to explainaspects within the scope of the appended claims, no limitation of theclaims should be implied based on particular features or arrangements insuch examples, as one of ordinary skill would be able to use theseexamples to derive a wide variety of implementations. Further andalthough some subject matter may have been described in languagespecific to examples of structural features and/or method steps, it isto be understood that the subject matter defined in the appended claimsis not necessarily limited to these described features or acts. Forexample, such functionality can be distributed differently or performedin components other than those identified herein. Rather, the describedfeatures and steps are disclosed as examples of components of systemsand methods within the scope of the appended claims. Moreover, claimlanguage reciting “at least one of” a set indicates that one member ofthe set or multiple members of the set satisfy the claim.

What is claimed is:
 1. A method of correcting asymmetry during a waferetching process, the method comprising: producing a plasma from a plasmasource, the plasma source comprising a plasma chamber and the ionextraction grid system, the ion extraction grid system configured toproduce an ion beam from the plasma, the ion beam having a central axis;supporting a wafer on a stage; scanning the wafer relative to the ionbeam along a scan path, wherein a scan velocity of the wafer is variedas the wafer travels along the scan path, wherein the scan velocitydecreases as an area of the wafer exposed to the ion beam decreases; andmodifying applied beam flux as a function of a position of the wafer. 2.The method of claim 1, further comprising rotating the stage about thecentral axis during at least a portion of the etching process.
 3. Themethod of claim 1, further comprising tilting the stage with respect tothe ion beam during at least a portion of the etching process.
 4. Themethod of claim 1, further comprising cooling the wafer during at leasta portion of the etching process.
 5. The method of claim 1, wherein thescan path is linear.
 6. The method of claim 1, wherein the scan path isnon-linear.
 7. The method of claim 1, wherein a center of the scan pathcoincides with a center of the ion beam.
 8. The method of claim 1,wherein a center of the scan path does not coincide with a center of theion beam.
 9. The method of claim 1, wherein modifying the applied beamflux as a function of a position of the wafer comprises adjusting ionbeam current.
 10. The method of claim 1, wherein modifying the appliedbeam flux as a function of a position of the wafer comprises inserting aplurality of physical blocks along the scan path to create an apertureand adjusting the aperture position to narrow the applied ion beam. 11.The method of claim 1, wherein modifying the applied beam flux as afunction of a position of the wafer comprises adjusting an amount oftime the wafer is exposed to the ion beam.
 12. The method of claim 1,wherein the scan velocity decreases as a distance between the wafer andthe ion beam increases during the scan.
 13. The method of claim 1,wherein the scan path comprising a scan out path from the first end ofthe ion beam to the second end of the ion beam and a scan back path fromthe second end of the ion beam to the first end of the ion beam, whereinthe scan out path is the same as the scan back path.
 14. The method ofclaim 1, wherein the scan path comprising a scan out path from the firstend of the ion beam to the second end of the ion beam and a scan backpath from the second end of the ion beam to the first end of the ionbeam, wherein the scan out path is different from the scan back path.15. The method of claim 1, wherein the scan path comprising a scan outpath from the first end of the ion beam to the second end of the ionbeam and a scan back path from the second end of the ion beam to thefirst end of the ion beam, wherein an endpoint of the scan out path isdifferent from an endpoint of the scan back path.
 16. The method ofclaim 1, wherein the scan path comprising a scan out path from the firstend of the ion beam to the second end of the ion beam according to ascan out velocity function and a scan back path from the second end ofthe ion beam to the first end of the ion beam according to a scan backvelocity function, wherein the scan out velocity function is differentfrom the scan back velocity function.
 17. The method of claim 1, whereinthe scan path comprising a scan out path from the first end of the ionbeam to the second end of the ion beam according to a scan out velocityfunction and a scan back path from the second end of the ion beam to thefirst end of the ion beam according to a scan back velocity function,wherein one of the scan out velocity function and the scan back velocityfunction varies as a function of time.
 18. The method of claim 1,wherein the scan path comprising a scan out path from the first end ofthe ion beam to the second end of the ion beam according to a scan outvelocity function and a scan back path from the second end of the ionbeam to the first end of the ion beam according to a scan back velocityfunction, wherein both the scan out velocity function and the scan backvelocity function vary as a function of time.
 19. The method of claim 1,wherein the scan path comprising a scan out path from the first end ofthe ion beam to the second end of the ion beam according to a scan outvelocity function and a scan back path from the second end of the ionbeam to the first end of the ion beam according to a scan back velocityfunction, wherein at least one of the scan out velocity function and thescan back velocity function vary within one scan path.
 20. The method ofclaim 1, wherein the scan path comprising a scan out path from the firstend of the ion beam to the second end of the ion beam according to ascan out velocity function and a scan back path from the second end ofthe ion beam to the first end of the ion beam according to a scan backvelocity function, wherein at least one of the scan out velocityfunction and the scan back velocity function vary each scan path. 21.The method of claim 1, wherein the scan path comprising a scan out pathfrom the first end of the ion beam to the second end of the ion beamaccording to a scan out velocity function and a scan back path from thesecond end of the ion beam to the first end of the ion beam according toa scan back velocity function, wherein both the scan out velocityfunction and the scan back velocity function vary each scan path. 22.The method of claim 1, wherein the scan velocity of the wafer is slowedas a center of the wafer travels along the far side of the scan path.23. The method of claim 22, wherein the scan velocity is asymmetric withrespect to the central axis of the ion beam.
 24. A method of correctingasymmetry during a wafer etching process, the method comprising:producing a plasma from a plasma source, the plasma source comprising aplasma chamber and the ion extraction grid system, the ion extractiongrid system configured to produce an ion beam from the plasma, the ionbeam having a central axis; supporting a wafer on a stage including atleast one of rotating the stage about the central axis and tilting thestage with respect to the ion beam during at least a portion of theetching process; scanning the wafer relative to the ion beam along ascan path in accordance with a scan velocity function, wherein a scanvelocity of the wafer is varied as the wafer travels along the scanpath, wherein the scan velocity decreases as an area of the waferexposed to the ion beam decreases; and modifying applied beam flux as afunction of a position of the wafer by varying the scan velocityfunction as the wafer travels along the scan path.
 25. The method ofclaim 24, wherein the scan velocity decreases as a distance between thewafer and the ion beam increases during the scan.
 26. The method ofclaim 24, further comprising: rotating the stage about the central axisduring at least a portion of the etching process; and tilting the stagewith respect to the ion beam during at least a portion of the etchingprocess.
 27. The method of claim 26, wherein modifying the applied beamflux as a function of a position of the wafer comprises inserting aplurality of physical blocks along the scan path to create an apertureand adjusting the aperture position to narrow the applied ion beam. 28.The method of claim 26, wherein the scan path comprising a scan out pathfrom the first end of the ion beam to the second end of the ion beamaccording to a scan out velocity function and a scan back path from thesecond end of the ion beam to the first end of the ion beam according toa scan back velocity function, wherein both the scan out velocityfunction and the scan back velocity function vary as a function of time.29. The method of claim 26, wherein the scan path comprising a scan outpath from the first end of the ion beam to the second end of the ionbeam according to a scan out velocity function and a scan back path fromthe second end of the ion beam to the first end of the ion beamaccording to a scan back velocity function, wherein at least one of thescan out velocity function and the scan back velocity function varywithin one scan path.
 30. The method of claim 26, wherein the scan pathcomprising a scan out path from the first end of the ion beam to thesecond end of the ion beam according to a scan out velocity function anda scan back path from the second end of the ion beam to the first end ofthe ion beam according to a scan back velocity function, wherein atleast one of the scan out velocity function and the scan back velocityfunction vary each scan path.
 31. The method of claim 26, wherein thescan path comprising a scan out path from the first end of the ion beamto the second end of the ion beam according to a scan out velocityfunction and a scan back path from the second end of the ion beam to thefirst end of the ion beam according to a scan back velocity function,wherein both the scan out velocity function and the scan back velocityfunction vary each scan path.
 32. The method of claim 26, wherein thescan velocity of the wafer is slowed as a center of the wafer travelsalong the far side of the scan path.
 33. The method of claim 32, whereinthe scan velocity is asymmetric with respect to the central axis of theion beam.
 34. A method of correcting asymmetry during a wafer etchingprocess, the method comprising: producing a plasma from a plasma source,the plasma source comprising a plasma chamber and the ion extractiongrid system, the ion extraction grid system configured to produce an ionbeam from the plasma, the ion beam having a central axis; supporting awafer on a stage; scanning the wafer relative to the ion beam along ascan path, the scan path comprising a scan out path from the first endof the ion beam to the second end of the ion beam according to a scanout velocity function and a scan back path from the second end of theion beam to the first end of the ion beam according to a scan backvelocity function, wherein one of the scan out velocity function and thescan back velocity function varies as a function of time, wherein a scanvelocity of the wafer is varied as the wafer travels along the scanpath, wherein the scan velocity decreases as an area of the waferexposed to the ion beam decreases; and modifying applied beam flux as afunction of a position of the wafer.
 35. The method of claim 34, furthercomprising rotating the stage about the central axis during at least aportion of the etching process.
 36. The method of claim 35, furthercomprising tilting the stage with respect to the ion beam during atleast a portion of the etching process.
 37. The method of claim 36,wherein modifying the applied beam flux as a function of a position ofthe wafer comprises inserting a plurality of physical blocks along thescan path to create an aperture and adjusting the aperture position tonarrow the applied ion beam.
 38. A method of correcting asymmetry duringa wafer deposition process, the method comprising: producing a plasmafrom a plasma source, the plasma source comprising a plasma chamber andthe ion extraction grid system, the ion extraction grid systemconfigured to produce an ion beam from the plasma, the ion beam having acentral axis; supporting a wafer on a stage; scanning the wafer relativeto the ion beam along a scan path, wherein a scan velocity of the waferis varied as the wafer travels along the scan path, wherein the scanvelocity decreases as an area of the wafer exposed to the ion beamdecreases; and modifying applied beam flux as a function of a positionof the wafer.
 39. The method of claim 38, further comprising rotatingthe stage about the central axis during at least a portion of thedeposition process.
 40. The method of claim 38, further comprisingtilting the stage with respect to the ion beam during at least a portionof the deposition process.
 41. The method of claim 38, furthercomprising cooling the wafer during at least a portion of the depositionprocess.
 42. The method of claim 38, wherein the scan path is linear.43. The method of claim 38, wherein the scan path is non-linear.
 44. Themethod of claim 38, wherein a center of the scan path coincides with acenter of the ion beam.
 45. The method of claim 38, wherein a center ofthe scan path does not coincide with a center of the ion beam.
 46. Themethod of claim 38, wherein modifying the applied beam flux as afunction of a position of the wafer comprises adjusting ion beamcurrent.
 47. The method of claim 38, wherein modifying the applied beamflux as a function of a position of the wafer comprises inserting aplurality of physical blocks along the scan path to create an apertureand adjusting the aperture position to narrow the applied ion beam. 48.The method of claim 38, wherein modifying the applied beam flux as afunction of a position of the wafer comprises adjusting an amount oftime the wafer is exposed to the ion beam.
 49. The method of claim 38,wherein the scan velocity decreases as a distance between the wafer andthe ion beam increases during the scan.
 50. The method of claim 38,wherein the scan path comprising a scan out path from the first end ofthe ion beam to the second end of the ion beam and a scan back path fromthe second end of the ion beam to the first end of the ion beam, whereinthe scan out path is the same as the scan back path.
 51. The method ofclaim 38, wherein the scan path comprising a scan out path from thefirst end of the ion beam to the second end of the ion beam and a scanback path from the second end of the ion beam to the first end of theion beam, wherein the scan out path is different from the scan backpath.
 52. The method of claim 38, wherein the scan path comprising ascan out path from the first end of the ion beam to the second end ofthe ion beam and a scan back path from the second end of the ion beam tothe first end of the ion beam, wherein an endpoint of the scan out pathis different from an endpoint of the scan back path.
 53. The method ofclaim 38, wherein the scan path comprising a scan out path from thefirst end of the ion beam to the second end of the ion beam according toa scan out velocity function and a scan back path from the second end ofthe ion beam to the first end of the ion beam according to a scan backvelocity function, wherein the scan out velocity function is differentfrom the scan back velocity function.
 54. The method of claim 38,wherein the scan path comprising a scan out path from the first end ofthe ion beam to the second end of the ion beam according to a scan outvelocity function and a scan back path from the second end of the ionbeam to the first end of the ion beam according to a scan back velocityfunction, wherein one of the scan out velocity function and the scanback velocity function varies as a function of time.
 55. The method ofclaim 38, wherein the scan path comprising a scan out path from thefirst end of the ion beam to the second end of the ion beam according toa scan out velocity function and a scan back path from the second end ofthe ion beam to the first end of the ion beam according to a scan backvelocity function, wherein both the scan out velocity function and thescan back velocity function vary as a function of time.
 56. The methodof claim 38, wherein the scan path comprising a scan out path from thefirst end of the ion beam to the second end of the ion beam according toa scan out velocity function and a scan back path from the second end ofthe ion beam to the first end of the ion beam according to a scan backvelocity function, wherein at least one of the scan out velocityfunction and the scan back velocity function vary within one scan path.57. The method of claim 38, wherein the scan path comprising a scan outpath from the first end of the ion beam to the second end of the ionbeam according to a scan out velocity function and a scan back path fromthe second end of the ion beam to the first end of the ion beamaccording to a scan back velocity function, wherein at least one of thescan out velocity function and the scan back velocity function vary eachscan path.
 58. The method of claim 38, wherein the scan path comprisinga scan out path from the first end of the ion beam to the second end ofthe ion beam according to a scan out velocity function and a scan backpath from the second end of the ion beam to the first end of the ionbeam according to a scan back velocity function, wherein both the scanout velocity function and the scan back velocity function vary each scanpath.
 59. The method of claim 38, wherein the scan velocity of the waferis slowed as a center of the wafer travels along the far side of thescan path.
 60. The method of claim 59, wherein the scan velocity isasymmetric with respect to the central axis of the ion beam.